Various metallic, plastics and ceramic materials have hitherto been used as an implant material for a bone or tooth in the orthopedic and dental fields. However, these conventional materials are not satisfactory since they are poor in compatibility to bone in a human or animal body.
Apatite is represented by the formula Ca.sub.10 (PO.sub.4).sub.6 (OH,F,Cl).sub.2, which may further contain 1 to 10% of carbonate ion (CO.sub.3.sup.--). Such an apatite substance constitutes a main component of the minerals of bones and teeth in vertebrate and has chemical properties such as being soluble in an acid, little or slightly soluble in water and highly stable in an alkali. It is known, on the other hand, that sintered apatite materials obtainable by sintering apatite at a high temperature have no toxicity and are excellent in compatibility to bone in a human or animal body. Therefore, the sintered apatite materials have increasingly become of great interest in the orthopedic and dental fields. However, the sintered apatite materials have insufficient mechanical strength, paricularly low impact strength, and therefore, must be improved in strength in order to make it possible to employ them as an implant material for a part to which body weight is to be loaded, for example (see, H. Aoki et al, Ceramics, "Apatite as a Biomaterial", 10 [7] 1975, PP. 57-66).